1. Field of the Invention
The present invention relates generally to submersible pumping systems, particularly those adapted for the separation of gas from liquids prior to the production of the liquid to the earth's surface.
2. Description of the Related Art
Submersible pumping systems are routinely used for the production of liquids, particularly hydrocarbons and water, to the earth's surface. These systems are particularly effective and efficient for producing liquids from those subsurface formations where liquids predominate over gas. In situations where gas is also present, the efficiency of the pumping process is frequently decreased because the pump tends to intake gas with the liquid causing the pump to cavitate. If enough gas is pulled into the pump, the pump may quit pumping liquid, a malady known as gas lock.
In gas lock, the pump fills with gas so that it does not generate sufficient pressure to pump the liquid to the surface, and flow stops. Resumption of pumping may be as simple as ceasing production so that the submersible pump can cycle or, in worse case situations, may require pulling the pumping system out of the production casing.
Cavitation and gas lock events are potentially traumatic to the workings of the submersible pumping system. These events can contribute to the wear and premature failure of both the pump and the motor, especially in combination with the excessive motor temperatures generated during gas lock episodes. Furthermore, it is costly in time and lost production whenever a submersible pump or motor must be serviced by pulling them from the well bore. Thus, avoidance of cavitation and gas lock increases pumping efficiency, reduces maintenance costs on the pump and motor, and decreases the cost of production of the target liquid.
Previously, single-stage gas separators have been used upstream of the pump in an effort to separate the gas from the liquid to be produced. Single-stage separators are most effective in formations having relatively low gas-to-liquid ratios. In these situations, gas separators have been effectively used to separate gas from the liquid before the liquid reaches the pump. Because gas and liquid are separated before reaching the pump, primarily liquid is fed to the pump, thus reducing the risk of cavitation and the possibility of gas lock and also maintaining the efficiency of the pumping process.
In formations having high gas-to-liquid ratios, the use of multiple-stage gas separators has been attempted. In this application, generally two gas separators are coupled in series upstream from the pump. These multiple-stage gas separators have not provided the desired results, particularly in high gas-to-liquid ratio formations.
Accordingly, an efficient and cost effective means is desired for the separation of gas from liquid for the production of the liquid of interest to the earth's surface, particularly from formations having a high gas-to-liquid ratio and those having a high flow rate.